This IPCP-HTM application constitutes three Research Projects, one Research Support Core and an Administration Core, under the direction of Principal Investigator, John P. Moore, PhD and co-Principal Investigator, Robin Shattock, PhD. The purpose of the program is to conduct in vitro and in vivo pre-clinical and animal model-based research intended to identify and characterize combinations of inhibitors of HIV-1 entry that might be suitable for development as topical microbicides, then test the most suitable candidates for safety in uninfected women. Our central hypothesis is that combinations of specific inhibitors of HIV-1 attachment, fusion and entry (AFE inhibitors) could prevent HIV-1 sexual transmission, when properly formulated and applied by women or men prior to intercourse. We believe microbicide design should be based on rational scientific principles, taking into account accumulated knowledge of the stages of the viral life cycle to be impeded, the mechanism of action of candidate inhibitors, and the biological processes involved in HIV-1 transmission. We do not intend to study microbicide candidates that act non-specifically, that have a broad-spectrum activity against multiple pathogens, or that are also spermicides. Our goal is to use our knowledge of virology and mammalian biology to help develop a mechanism-based, HIV-1-specific microbicide(s). Hence, we will evaluate combinations of different inhibitors of defined stages in HIV-1 entry. We will move the best inhibitors into a safety trial in the later years of the project. We propose: Research Project I: Robin Shattock. Characterization of HIV-1 AFE inhibitors in human cervical and rectal tissue models; Research Project II: Melissa Pope. Assessment of AFE inhibitors in DC-T cell mixtures; Research Project III: Ronald Veazey. Evaluation of AFE inhibitors for protection from SHIV vaginal challenge in macaques; Research Project IV: Charles Lacey. Safety studies of AFE inhibitors in normal women; Core A: John P. Moore. Inhibitor Acquisition, Evaluation and Formulation; Core B: John P. Moore. Administration.